Silver halide photographic light-sensitive materials, which are also referred to as silver halide photographic materials, hereinafter, have so far been widely used as materials capable of providing images of high and consistent quality at low prices. Recent years have also seen progress of digitization at an accelerated pace in the field of color prints utilizing silver halide color photographic materials. For instance, widespread usage of digital exposure, typified by laser scanning exposure, has grown dramatically, in contrast to traditional analog exposure, by which direct printing from processed color negative films is performed via a color printer. Digital exposure features image processing that permits production of high-quality prints, and it plays an important role in improving qualities of prints utilizing silver halide color photographic materials. As digital camera penetration increases, it also becomes an important factor for high-quality color prints to be easily obtained from electronic recording materials. Under these circumstances, digital exposure is expected to come into wider use.
On the other hand, printing technologies, including inkjet printing, dye-sublimation printing, and color xerography, have made respective strides to be at a level of producing photographic print quality, and they are on their way to being recognized as color print systems. Of these competing print systems, the print system that combines silver halide color photographic materials and digital exposure provides advantages in high image quality, high productivity, and guarantee of high fastness for images. Therefore, it is desired to expand these advantages and to offer high-quality print services at low prices in a short time.
For instance, if it becomes possible to offer one-stop service of color prints, such that a recording medium bearing data taken by a digital camera is received over the counter, printing from the recording medium is finished in a short turnaround time, on the order of several minutes, and the recording medium is returned together with prints of high quality, then, color prints using silver halide color photographic materials can gain higher superiority than ever. In addition, if rapid processing suitability of silver halide color photographic materials is further improved, processing devices can be downsized, to result in production of printing equipment having high productivity while being compact and inexpensive, and it can be expected that one-stop service of color prints will become increasingly pervasive.
In addition, requirements for curtailments and speeding up of processing processes have grown in recent years. The purpose of these requirements is to further enhance high productivity, which is one point of superiority of the print production system using color photographic paper over other color print systems, such as inkjet and dye-sublimation systems.
Therefore, it is necessary to study silver halide color photographic materials from various viewpoints, including viewpoints of reducing the exposure time, reducing the time lapse between the end of exposure and the start of development (so-called latent-image time), reducing the processing time, and reducing the drying time after processing. For reductions in those individual times, various suggestions have been made until now.
Silver halide emulsions incorporated in silver halide color printing photographic materials are required to meet various requirements as mentioned above. As to halide composition, silver halide emulsions having high silver chloride contents (also referred to as “silver-chloride-rich emulsions”) are adopted in response to the rapid processing requirement. Further, it is known that the development speed is increased by reducing the size of emulsion grains (also referred to as “grain diameter”) contained in a silver halide emulsion, and techniques relating thereto are already disclosed (See, e.g., abstracts of papers read at The 2004 Autumn Convention of The Society of Photographic Science and Technology of Japan, (pages 20-21)). However, reducing the size of emulsion grains also causes a drop in sensitivity, which causes the problem that the sensitivity necessary for digital exposure cannot be attained. This being the case, techniques for increasing sensitivities of silver-chloride-rich emulsions have been required.
In recent years, arts of increasing sensitivities of photograph-taking color photosensitive materials by using selenium (Se) compounds for chemical sensitization have been widely known and adopted. However, it has also been known that the use of selenium compounds is liable to cause an increase in fogging, so techniques for improving this situation have also been-studied.
In the case of color negative films as recording materials, however, an increase in fogging can be corrected substantially as part of mask density at the time of printing, even when the fogging of silver halide emulsions is somewhat increased. With color reversal films also serving as viewing materials, on the other hand, the fogging of silver halide emulsions results in a lowering of the maximum density (Dmax), on account of the image formation method adopted therein, so a little change becomes substantially insignificant.
In contrast to the above cases, an increase in fogging of silver halide emulsions results in color stains on a white background area, in the case of color printing photographic materials, typified by color paper, and so it becomes a significant defect. Even a slight increase in fogging results in fatal quality loss. In other words, it is required for color printing photographic materials to ensure a good-quality white background not only immediately after production but also after prolonged storage. Likewise, it is required for them to cause no increase in fogging even when subjected to rapid processing. Therefore, antifogging requirements become very severe when selenium compounds are used in silver-chloride-rich emulsions intended for use in silver halide color printing photographic materials.
Since silver iodobromide emulsions are exclusively used in photograph-taking color photosensitive materials, antifogging techniques in the case of using selenium compounds are also limited to the technical disclosures in the region of those emulsions. Further, these techniques are insufficient to meet the aforesaid severe requirements.
Very recently, techniques to attain compatibility between digital exposure and rapid processing, in the case of using a silver-chloride-rich emulsion and a selenium compound, have been studied. A technique for providing emulsions that can ensure high sensitivity and high contrast when they are subjected to high illumination intensity exposure or laser scanning exposure, as well as reduced fogging and an excellent white background even with rapid processing, is disclosed in JP-A-2003-287838 (“JP-A” means unexamined published Japanese patent application). While this reference demonstrates the effect of making improvement in photographic fog immediately after the production of silver halide color photographic materials, it makes no mention of improving storability on the assumption that the sensitive material would undergo changes by aging. Further, it has a description of gradations in the cases of 10-second exposure and 10−4-second exposure, but they are expressed in relative values to a standard sample. Accordingly, the present invention cannot be anticipated by that description.
Although JP-A-4-335336 and JP-A-4-335338 describe gradations in the cases of 10-second exposure and 10−2-second exposure, the concerns of their technical disclosures are improvements in pressure characteristic and latent-image storability, respectively, and they do not mention fogging.
JP-A-6-308652 relates to improvements in storability, and discloses the art of reducing photographic fog that develops with aging. Although laser scanning exposure is described therein, its influences on gradation are not clarified. In addition, mention is made of rapid processing, but no disclosure is made in the Examples.
Silver halide emulsions used in color photographic printing paper are silver halide emulsions with high silver chloride contents to meet demands for rapid processing. While photosensitive materials with high silver chloride contents are advantageous to rapid processing in particular, they have disadvantages of low sensitivity and difficulty in both chemical sensitization and spectral sensitization, their sensitivities attained are labile, and they tend to bring about photographic fog. In addition, it is known that the rapid processing suitability can be further enhanced by use of silver halide emulsions having small grain sizes. As to spectrally sensitized emulsions, however, their sensitivities are proportional to the surface areas of silver halide grains, so reduction in grain size of silver halide results in a significant drop in sensitivity. Accordingly, further increase in sensitivity is required to enhance rapid processing suitability.
To improve high illumination intensity failure of a silver chloride emulsion and attain hard gradation under high illumination intensity, it is known to dope the emulsion with iridium. However, an iridium-doped silver chloride emulsion is known to undergo latent-image sensitization in a short time after exposure, and JP-B-7-34103 (“JP-B” means examined Japanese patent publication) discloses that the problem of latent-image sensitization is solved by preparing localized phases having high silver bromide contents, and doping them with iridium. Although the silver halide emulsions prepared according to such a method can provide high sensitivity and hard gradation and avoid causing the problem of latent-image sensitization even when they undergo exposure with relatively high illumination intensity for a time on the order of 1/100 second, it has been discovered that they caused a problem of reducing their tendency toward hard gradation, in the case of aiming to retain high sensitivities up to the level of 1μ-second ultrahigh illumination intensity exposure required in digital exposure systems utilizing laser scanning exposure.
U.S. Pat. Nos. 5,783,373 and 5,783,378 disclose a method of gradation hardening in which at least three kinds of dopants are used to reduce high illumination intensity failure. However, hard graduation is obtained because of using a dopant having functions of desensitization and hard graduation. Accordingly, this method is incompatible fundamentally with enhancement in sensitivity.
As mentioned above, further increase in sensitivity is required for color photographic printing paper also. To increase the sensitivities of silver-chloride-rich emulsions, various improvements in chemical sensitization methods and methods of forming silver halide emulsion grains have been made. As typical methods for chemical sensitization of silver halide emulsions, various sensitization methods, including sulfur sensitization, selenium sensitization, tellurium sensitization, sensitizations using precious metals such as gold, reduction sensitization, and combinations of these sensitizations, have been developed.
To mention selenium sensitization, in particular, of those sensitization methods, it is known that selenocarboxylic acid esters, i.e. seleno esters, are usable as selenium sensitizers (e.g. in U.S. Pat. Nos. 3,297,446 and 3,297,447, and JP-B-57-22090). Generally speaking, selenium sensitization produces a greater sensitization effect than sulfur sensitization carried out in the photographic industry, but it brings about a great degree of fogging and tends to enhance soft gradation. Therefore, selenium sensitization has been unsuitable for color photographic printing paper.
Most of the patents hitherto disclosed, though instrumental in improving such defects, do not deal with the problem of fogging associated with variations in processing factors. Laboratories on the market are not always under satisfactory processing-solution management, and sometimes photographic processing is performed under situations in which the replenishment rate, pH setting, processing temperature, and washing condition deviate from their respective correct values. When selenium sensitization, in particular, is applied, there occurs a serious problem that changes in processing temperature and processing pH, as well as the mixing of a bleach-fix solution into a color developer, tend to cause variations in fogging, and the qualities of finished photographs are dependent to great degrees on them.
An important property required for color photographic printing paper to ensure high-quality color prints is the ability to reproduce not only colors with high saturation and reduced dullness but also higher gray densities. High saturation of reproduced colors makes it possible to express vivid color tones, and reproduction of high gray densities makes it possible to express extended perspective images. As long as color photographic printing paper has the ability to reproduce colors with reduced dullness and high saturation, colors lower in saturation can be produced via image processing on a computer. Conversely, colors higher in saturation cannot be reproduced if color photographic printing paper does not have the ability to reproduce colors higher in saturation. Since gray images are produced by simultaneous development of yellow, magenta, and cyan colors, it becomes possible to reproduce higher gray densities by heightening every developed color density.
Our study found that, although application of selenium sensitization certainly increased the sensitivity under rapid processing, in some cases streaky unevenness showed up in prints obtained, or color saturation is lowered, or gray densities were lowered.
In color photographic printing paper, use of silver halide emulsions least susceptible to fogging is suitable for expressing white color beautifully. Although there may be cases in which selenium sensitization exhibits a greater sensitization effect than the sulfur sensitization carried out in the photographic industry, selenium sensitization was unsuitable for color photographic printing paper, because it caused a considerable degree of fogging and was apt to enhance soft gradation. In addition, the combined use of selenium sensitization and gold sensitization results in a remarkable sensitivity increase, but at the same time, it causes a great rise in fogging and soft gradation enhancement. As such, it has been desired intensely to develop selenium sensitization capable of ensuring fog reduction and hard gradation.
In still more rapid processing, which has been urgently required in recent years, imparting rapid processing suitability to photosensitive materials tends to cause dullness in developed colors. In addition, there has been a strong request for running processing suitability. As such, further improvements in these abilities have been intensely desired.
In the case of processing a great many sheets of photosensitive material, the first sheet and the last sheet are required to have equivalent print quality. On the other hand, selenium sensitization of photosensitive materials occasionally causes a problem of print reproducibility, or running processing suitability. As such, it becomes necessary to improve the running processing suitability.
Depending on the type of yellow coupler that is used, there may be cases in which a sensitivity difference is caused by the difference in the emulsion-making scale (which is an indication of the amount of an emulsion made and expressed in silver content therein, in moles). In general, there is apprehension that the sensitivity difference caused by a difference in the emulsion-making scale gives rise to a difference in print reproducibility.
Other and further features and advantages of the invention will appear more fully from the following description.